Further research yields this better answer:
To do this in Splunk Enterprise 6.0, use ui-prefs.conf. If you set the value in $SPLUNK_HOME/etc/system/local, all your users should see it as the default setting. For example, if your $SPLUNK_HOME/etc/system/local/ui-prefs.conf file includes:
[search]
dispatch.earliest_time = @d
dispatch.latest_time = now
The default time range that all users will see in the search app will be today.
The configuration file reference for ui-prefs.conf is here: http://docs.splunk.com/Documentation/Splunk/latest/Admin/Ui-prefsconf
We are updating the Search Manual to include this information.
I am leaving the flashtimeline workaround information here in case it's useful to people for other reasons.
